High-voltage DC battery packs may be used to energize electric machines in a variety of different torque-generating systems. For instance, the output torque from an electric motor may be used to rotate an input member of a power transmission in a hybrid electric or plug-in electric vehicle, i.e., a vehicle having a battery pack that may be selectively recharged using a charging outlet or offboard power supply. The individual battery cells of a given battery pack gradually age and degrade over time. As a result, battery performance parameters such as open circuit voltage, cell resistance, and state of charge may change relative to calibrated/new values. Battery degradation is therefore monitored by a designated battery controller in order to estimate the remaining amount of battery power capability. The battery power capability estimates thereafter can be used to make powertrain mode selection decisions or to perform other control actions.
Existing battery control methodologies seek to protect relatively weak battery cells in a battery pack, i.e., those battery cells exhibiting the lowest cell voltages during a discharge event or the highest cell voltage during a charge event. Typically, battery protection is achieved by controlling the battery pack voltage in such a way that the lowest cell voltages are forced to remain above a minimum allowed pack voltage. In other words, the battery pack voltage is reactively adjusted in response to a given battery cell approaching or dropping below a voltage control limit or floor. However, changing a voltage control limit, particularly during a power pulse, can reduce the accuracy of battery power capability estimates.